Uli Heber Subluminous O stars Origin and evolutionary links Hydrogen-Deficient Stars, Tübingen

Outline  Early results  Atmospheric parameters  Evolutionary scenarios - Close binary evolution (RLOF, CEE & WD mergers) vs - Delayed core helium flashers - (non-core helium-burning stars)  Kinematics  Summary & Outlook

sdO vs. sdB stars sdO sdB sdB stars: - helium-deficient - „cool“: 20-40kK sdO stars: - H-deficient - Hot > 40kK - He-sdOs: No hydrogen

Subluminous O and B stars Greenstein & Sargent (1974)

sdB stars: He-deficiency from diffusion Metal abundances HST/STIS UV spectra -Enrichment of heavy elements (>100 times) except Fe -Radiative levitation Fe Pb O´Toole & Heber 2006 CPD PB/ 208 PB =solar

Post-EHB vs post-AGB evolution sdB = Extended Horizontal Branch stars: - He-burning core & inert H-envelope (<0.01 Msun) - How to loose the envelope? - sdO stars=post-EHB? Post-AGB Objects: -rare -linked to RCrB/EHe stars

sdB sdO Convective transformation (Wesemael et al. 1982) Groth et al. (1985): Convection occurs in He-rich atmo- spheres only Convection He/H=1 sdO sdB

Hot subdwarfs from UVX Surveys LTE- spectroscopic analyses of sdB stars: - Palomar Green survey: Saffer et al. 1994, Maxted et al Hamburg Quasar Survey: Edelmann et al ESO-Supernova Progenitor Survey (SPY): Lisker et al NLTE spectroscopic analyses of sdO-stars: - SPY (Ströer et al. 2007) - Sloan Digital Sky Survey (Hirsch et al. 2007) atmospheric parameters for >200 sdB atmospheric parameters for 130 sdO

Fits of UVES-spectra (SPY): sdO high resolution spectra, TMAP NLTE models, H&He sdOHe sdO

Fits of SDSS-spectra: sdO sdOHe sdO

SPY: C & N lines solar - C&N strong: diamonds - C strong: triangle - N strong - no C or N: open - All He-rich sdOs have C and/or N -None of the He-poor have C/N

Carbon III/IV SPY: n(C)=0.13% (Hirsch et al. 2007) v rot sin i=0 km/s

Carbon III/IV SPY: n(C)=0.25% (Hirsch et al. 2007) v rot sin i=20 km/s

solar SPY He-poor He-rich

The canonical picture He-ZAMS Smooth evolutionary time scales: - He-poor scattered in diagram progeny of sdB stars - Clumping of He-rich sdOs can not be explained

SPY&SDSS: sdB, sdO & He-sdO sdO stars: He-sdO: clumping at -Teff = 45000K -log g = 5.8 sdB He-sdO clump SPY-sds: without error bars

Post EHB EHB He-ZAMS Sub- He-ZAMS SPY&SDSS: sdB, sdO & He-sdO

Hot He flashers Delayed He core flash Canonical evolution Sweigart, 1987 Core flash

Delayed helium shell flash He sdO

Very late helium core flash He sdO He/C Could explain He-sdOs below the Helium ZAMS

sds in binaries  mostly single-lined: RV curve:  mass function SPY: fraction of close binaries: radial velocity variables with P<10d sdBs; :40% (Napiwotzki et al.,2005) Minimum mass of companion Napiwotzki et al sdOs: 4% RVV (from SPY)

Period distribution Nature of companions: white dwarf or low mass m.s. stars WDWD MS unknown Morales-Rueda (2006)

Binary Population Synthesis (BPS) Han et al. (2003) a: 1. CE ejection b: 1. stable RLOF c: 2. CE ejection d: merger of two helium white dwarfs

Comparison to Han et al. (HPMM) sdBs: best match: models with correlated masses and low CEE efficiency Poor match: models with 100% CEE efficiency O-types: He-rich sdOs: stars clump at 45000K, too hot for any HPMM simulation set He-poor sdO: scattered in (Teff, log g) diagram Ströer et al. 2007

Non core helium-burning evolution Castellani, Castellani & Moroni (2006) M=0.8 Msun η=0.75 Star leaves RGB Before helium ignites in the core (e.g. by mass tranfer to a companion) Cooling tracks to form helium white dwarfs

Non-core helium-burning sdB stars HD (V=10.2) (Heber et al., 2001) - Hipparcos parallax - distance = 80 pc - mass = 0.22 M sun No helium burning - companion: M>0.72M sun Tracks: Driebe et al.

A Hyper-velocity star (HVS) amongst sdO stars from SDSS HVS km/s Galactic restframe velocity

SMBH Slingshot Hills (1988):  Disruption of a binary near a Super- Massive Black Hole releases companion at up to 1000 km/s or more.  Detection of a single HVS: evidence for a SMBH Gualandris et al. (2005)

Summary & Conclusion  Origin of sdB/sdO stars? (i) delayed core helium flash (ii) close binary evolution (RLOF & CEE ejection), mergers of He-WDs He-poor sdOs are the progeny of sdB stars He-rich sdO stars are hotter than predicted by (i) & (ii) atmospheres: No metal line blanketing metalicity effects evolution (Brown et al. 2007) Post-AGB-evolution & Non-core He-burning evolution: rare due to short evolutionary time scales

Outlook: A pulsating sdO star Strongest mode: P=119.3 s A=38.6 mmag plus - First Harmonic plus - 8 modes: s Woudt et al. (2001)

Stellar & Envelope Masses Masses: 0.45 to 0.55 M sun Envelope masses: M sun sdB

Thank You!

sdB Asteroseismology Multi-periodic light variations (few mmag) at periods from 2 to 10min. Østensen et al. (2001)

Carbon and Nitrogen SPY: C and/or N lines Detected - in all helium-rich - In none of the helium-poor ones (Ströer et al. 2007)

Carbon abundances

Challenges  Observations: better statistics, better data: the quest for high resolution. metal abundances (see Poster 25)  Evolution theory: Prediction of surface abundances for late hot flasher (Cassisi et al. 2003) & He WD mergers  Angular momentum and stellar rotation  Stellar atmospheres & envelopes: diffusion (rad. levitation) & metal line blanketing, see talk by G. Michaud  Mass loss and diffusion  The role of magnetic fields (O´Toole et al. 2005)

Grazie!

Blue Hook stars

HD128220B: Fe & Ni Fe/H=1/100 solar Ni/H=1/10 solar

US 708: Keck LRIS spectrum T eff = 45500K, log g = 5.23, mass = 0.5 M o B=19.0 mag Distance: 19 kpc

Run-away stars  Ejection scenario: born in the plane and ejected (Blaauw, 1961) - binary supernova ejection - 3 body interaction in an open cluster  Calculate path and time of flight: - radial velocities, distances & proper motion - orbit integrator: Odenkirchen & Brosche (1992) - Galactic potential: Allen & Santillan (1991)

BD (Lanz et al. 1997) - Slight enrichment of Fe&Ni -fully metal line blanketed models: Teff lower by 6000K than metal free models

Metallicity effects on atmospheric parameters for the sdB SB 707 Solar ([m/H]=0.0): Teff = 33940K log g= 5.82 log He/H= *solar ([m/H]=+1.0) : Teff = 35380K log g= 5.90 log He/H=-2.91 Metal line blanketed LTE models

Summary II Heavy metals in sdO and sdB stars:  Non solar abundances of Fe & Ni in sdO stars  Non solar Ni/Fe (>solar)  Strong enrichment of many iron group elements in hot sdB stars (except Fe), about solar in “cool” sdBs (<30000K): FUV flux suppression UV upturn  Teff scale significantly changed by supersolar metal abundances (line blanketing)

Outlook: Radial velocities Vrad=700Km/s Hypervelocity star

Cosmic accelerator? Ejection from a cluster by three body interaction? SN II in a binary release companion at orbital velocity? Supermassive black hole in the Galactic center? Better ideas??

HQS-sdB: comparison with Han et al.

Trends of helium abundance sdB sdO He sdO solar  sdB stars: - 2 sequences  sdO stars: - Spread by 6 orders of magnitude - 1/3 helium- deficient!

sdB Helium abundances Edelmann et al Two sequences: He/H vs. T eff

Hamburger Quasar Survey sdB stars: Edelmann et al. 2003: 100 sdB stars

sdB = Extreme HB stars Saffer et al EHB Post-EHB

The lower sequence Tracks from Driebe et al. (1998) M core

sdB and sdO stars from SPY SPY: ESO-VLT+UVES: High-res. Spectra of >1000 Double degenerate candidates - sdB: 79 (Lisker et al. 2005) - He-sdO: 30 (Ströer et al. sdO: ) - fraction of RV variables (P<10d): sdB: 39% He-sdO: 4% (1 SB2 binary) sdB

Trends and Sequences

Combining all studies Neglecting selection bias SDSS sdBs: To be done sdB Gap ? SPY-sds: no error bars shown

BPS Han et al: Binary population synthesis a)Without GK selection b)With GK selection

M 15 UV

Post EHB & post-AGB evolution Post-AGB Post EHB

UV spectroscopy of HB stars Caloi, Castellani et al Heber et al IUE

SDSS-sdOs Atmospheric models: - NLTE: - H+He, no metals - PRO2 code (Dreizler &Werner) - improved He atomic models - temperature correction scheme (Dreizler, 2003) sdO He sdO

Globular Cluster CMDs Moehler (2000) NGC 2808 (Walker, 1999) Blue hoo k

NGC 6752: HB &EHB stars Moni-Bidin et al. (2007) LTE spectral analyses: T eff, logg g match (E)HB prediction Helium subsolar

EHB Models Castellani et al Helium core mass: 0.47 M sun depen- ding on He and metal abundance (fixed by onset of He core flash) Horizontal Branch= sequence of envelope mass M env, EHB=very low M env (0.01 M sun ), inert H-rich envelope avoids AGB evolutions

Origin of EHB stars Castellani & Castellani 1993 M=0.8 Msun η=0.75 EHB-progenitor stars must loose almost their entire envelope by the time of the helium core flash strong RGB mass loss; Low mass stars (Pop. II, globular cluster): Very efficient RGB Reimers wind may be sufficient. Younger populations, i.e. more massive progenitors (field): ?

KPD : sdB + massive WD Billeres et al, 2000 Maxted et al. 2000, Geier et al. 2007

Candidate SN Ia Progenitor KPD : Total mass=1.4 Msun (Chandrasekhar mass) -Double degenerate -System merges within years -SN Ia explosion? (Geier et al. 2007) More on massive compaions: talk by Stephan Geier

sdB Asteroseismology Non-radial p-mode Pulsationa driven by Iron opacity bump: Predicted instability Strip matches Observations Charpinet et al. (2001)

sdB Asteroseismology Period matching technique: Linear theory: Amplitudes can not be predicted (PG1325+, Charpinet et al. 2006)

Metal abundances: Fe & Ni Feige 34: He-poor sdO Teff=60kK Fe/H=10*solarN i/H=70*solar

sdB Asteroseismology (PG1325, Charpinet et al. 2006) Model parameters: T eff, log g, M total, M env

sdB Asteroseismology PG : Time resolved spectroscopy (9000 spectra) Radial velocity variations (O´Toole et al. 2005): 20 periods (few km/s) Line profile variations (phase folded, Tillich et al. 2007):

sdB Asteroseismology Dominant mode: Teff semi-amplitude: 800K Log gsemi-amplitude: 0.08 First harmonic detected Cleaning for dominant mode: 8 weaker modes detected

sdO stars from SDSS candidates selected from all releases according to colour: u-g<0.2 (0.4) g-r<0.1  spectra:  40 sdO + 43 He sdO (Hirsch, Dipl. Thesis) Fits with NLTE models He sdO

The two sequences

Tracks from Dorman et al. (2003) with Z=0.02

The upper sequence Tracks from Dorman et al. (2003)

The lower sequence Tracks from Dorman et al. (2003)

Early NLTE Analyses : sdO Classification: He II > He I He-sdO: no Balmer detectable to the eye C and/or N strong sdO: otherwise Hunger et al Heber (1987) Post-EHB Post-AGB

Evolution of hot subluminous stars: the canonical picture SdB + sdO stars: Extreme Horizontal Branch stars EHB HB sdB sdO Dorman et al. (1993, ApJ 419, 596)

He-rich sdOs: - diamonds: C&N strong - C strong triangles -N strong - (triangles)

The lower sequence Tracks from Driebe et al. (1998) M core